Surface Precipitation and Passivation on Ultrafine- Grained Titanium in Physiological Solution

This investigation is an attempt to understand how the microstructures of Ti substrate affects the
chemical composition change and the repassivation of the titanium surface immersed in simulated
body fluid solution with bovine serum albumin added. Commercial pure titanium (CP-Ti) and Ti-0.2Pd
were used as objectives. Equal channel angular pressing was carried out for the grain refinement of
both metals. Some titanium specimens were subjected to heat-treatment for producing different
microstructures for comparison. Electrochemical impedance spectroscopy (EIS) was measured for the
evaluation of the corrosion resistance and passivation behavior. The surface compositions and
morphologies were examined by X-ray photoelectronic spectroscopy and scanning electron
microscopy. The solution used in the corrosion and immersion tests was pure N2 bubbled simulated
body fluid. The results of corrosion tests showed higher corrosion resistance of ECAP Ti-0.2Pd than
ECAP CP-Ti. Insignificant Warburg impedance indicated porous layer formation on ECAP titanium
and consequently easy transformation of ions and corrosion product through layer. The results of
immersion tests showed more precipitated particles formed on ECAP metals than on the heat-treated
metals. Enhanced precipitates were found formed on ECAP Ti-0.2Pd which is due to increased
hydrogen evolution reaction of Ti-0.2Pd compared to ECAP CP-Ti. The precipitation was composed of
C, N, O, Ti, Ca and P. More Ca, P, Ti and O contents in the surface deposition on ultrafine grained Ti
do benefit to the bioactivity improvement of Ti implant practically. This finding provides a method for
improving bio-bonding between implant and surround tissue.